Monolithic double balanced microstrip mixer with flat conversion loss

Abstract

A double balanced microstrip mixer circuit for a monolithic microwave integrated circuit comprising a diode ring modulator coupled to a first balun for supplying radio frequency signals to the mixer circuit and a second balun for supplying a signal generated locally to the mixer circuit, two outputs leading from the diode ring modulator for providing an intermediate frequency signal, a first pair of circuits coupled between the first balun and the diode ring modulator and a second pair of circuits coupled between the second balun and the diode ring modulator, for enabling broadband frequencies to be applied to the diode ring modulator independent of impedances created by the first and second baluns. The circuit further includes two low pass filters each coupled to one of the two outputs for rejecting unwanted feed through and a in-phase combiner coupled to the low pass filters.

I claim: 
     
       1. In a double balanced mixer circuit of the type comprising a diode ring modulator, a first balun having a first impedance coupled to said diode ring modulator for supplying radio frequency signals to said mixer circuit, a second balun having a second impedance coupled to said diode ring modulator for supplying a signal generated locally to said mixer circuit, and at least one output leading from said diode ring modulator for providing an intermediate frequency signal, the improvement comprising: first circuit means including passive microstrip means for providing a relatively broadband radio frequency short circuit over an intermediate frequency signal band coupled between said first balun and said diode ring modulator and second circuit means including passive microstrip means for providing a relatively broadband radio frequency open circuit over said intermediate frequency signal band coupled between said second balun and said diode ring modulator, for enabling broadband frequencies to be applied to said diode ring modulator independent of the impedance of said first and second baluns.   
     
     
       2. The balanced mixer circuit according to claim 1, wherein said intermediate frequency signal produced at said at least one output includes undesirable mixing products of said radio frequency signals and said signal generated locally and further comprising filter means coupled to said at least one output for rejecting unwanted feed through of said undesirable mixing products and for passing said intermediate frequency signal. 
     
     
       3. The balanced mixer circuit according to claim 2, wherein said at least one output comprises two outputs each producing said intermediate frequency signal and further comprising combiner means coupled to said filter means for combining said intermediate frequency signals which are passed through said filter means. 
     
     
       4. The double balanced mixer circuit according to claim 1, wherein said mixer circuit is implemented as a microstrip monolithic microwave integrated circuit. 
     
     
       5. The balanced mixer circuit according to claim 4, wherein said mixer circuit provides less than plus or minus one dB conversion loss flatness over a one and a half octave intermediate frequency band. 
     
     
       6. The balanced mixer circuit according to claim 5, wherein said mixer circuit provides less than plus or minus 0.5 dB conversion loss flatness over a one octave intermediate frequency band. 
     
     
       7. The double balanced mixer circuit according to claim 1, wherein said mixer circuit is implemented as a hybrid microwave integrated circuit. 
     
     
       8. A double balanced mixer circuit for a monolithic microwave integrated circuit, comprising: a diode ring modulator;   a first balun coupled to said diode ring modulator for supplying radio frequency signals to said mixer circuit;   a second balun coupled to said diode ring modulator for supplying a signal generated locally to said mixer circuit;   two outputs leading from said diode ring modulator each providing an intermediate frequency signal;   a first pair of circuits each comprising passive microstrip means for providing a relatively broadband radio frequency short circuit over an intermediate frequency signal band, said first circuits being coupled between said first balun and said diode ring modulator; and   a second pair of circuits each comprising passive microstrip means for providing a relatively broadband radio frequency open circuit over said intermediate frequency signal band, said second circuits being coupled between said second balun and said diode ring modulator.   
     
     
       9. The balanced mixer circuit according to claim 8, wherein said intermediate frequency signals produced at said two outputs each include undesirable mixing products of said radio frequency signals and said signal generated locally and further comprising filter means coupled to said two outputs for rejecting unwanted feed through of said undesirable mixing products and for passing said intermediate frequency signals. 
     
     
       10. The balanced mixer circuit according to claim 9, further comprises combiner means coupled to said filter means for combining said intermediate frequency signals which are passed through said filter means. 
     
     
       11. The balanced mixer circuit according to claim 8, wherein said mixer circuit provides less than plus or minus one dB conversion loss flatness over a one and a half octave intermediate frequency band when implemented as said monolithic microwave integrated circuit. 
     
     
       12. The balanced mixer circuit according to claim 8, wherein said mixer circuit provides less than plus or minus 0.5 dB conversion loss flatness over a one octave intermediate frequency band when implemented as said monolithic microwave integrated circuit. 
     
     
       13. A double balanced mixer circuit comprising: a diode ring modulator;   a first balun having a first impedance coupled to said diode ring modulator for supplying radio frequency signals to said mixer circuit;   a second balun having a second impedance coupled to said diode ring modulator for supplying a signal generated locally to said mixer circuit;   two outputs leading from said diode ring modulator each providing an intermediate frequency signal;   a first pair of circuits each comprising passive microstrip means for providing a relatively broadband radio frequency short circuit over an intermediate frequency band, coupled between said first balun and said diode ring modulator; and   a second pair of circuits each comprising passive microstrip means for providing a relatively broadband radio frequency open circuit over said intermediate frequency band, coupled between said second balun and said diode ring modulator;   wherein said first and second pair of circuits enable broadband frequencies to be applied to said diode ring modulator independent of the impedance of said first and second baluns.   
     
     
       14. The balanced mixer circuit according to claim 13, wherein said intermediate frequency signal produced at each of said two outputs includes undesirable mixing products of said radio frequency signals, and said signal generated locally and further comprising filter means coupled to said two outputs for rejecting unwanted feed through of said undesirable mixing products and for passing said intermediate frequency signals. 
     
     
       15. The balanced mixer circuit according to claim 14, further comprises combiner means coupled to said filter means for combining said intermediate frequency signals received from said filter means. 
     
     
       16. The balanced mixer circuit according to claim 13, wherein said mixer is implemented as a monolithic microwave integrated circuit which provides less than plus or minus one dB conversion loss flatness over a one and a half octave intermediate frequency band and less than plus or minus 0.5 dB conversion loss flatness over a one octave intermediate frequency band.